In the field of manufacturing integrated circuit elements, photo-lithographic process is essential. In order to attain a higher degree of integration in manufacturing the integrated circuit elements, patterning technology to form still finer patterns by the photo-lithographic process has been studied and, in recent years, such studies have lead to development of a technology enabling submicron-ordered fine patterning. In such photo-lithographic process, a photoresist is applied to a substrate, a latent image of a mask pattern is created in the photoresist using a reduction projection exposure apparatus, then the latent image is developed using a proper developer solution to obtain a patterned resist with the desired width and pattern. However, many substrates used in the field of manufacturing integrated circuit elements have such a high reflectivity that, upon exposure, exposing light passing through the photoresist layer is reflected on the surface of the substrate and is again incident into the photoresist layer, which causes problems that desired patterns are not obtained or that patterns with some defects are formed due to the exposure by the reflected light of photoresist areas which is not to be exposed originally or due to the existence of standing wave formed by interference between the reflected light and the incident light. Various techniques have been investigated to solve the problems. For example, there have been attempted a technique of addition of dye having absorption at the exposure wavelength into the resist to reduce the amount of light passing through the resist and consequently reduce the amount of reflected light, and a technique of forming an antireflective layer between the resist and a substrate in order to prevent light reflection from the substrate into resist by absorbing light having reached to the surface of the substrate upon exposure. As the latter type techniques, there are illustrated a technique of forming a coating of an inorganic compound having radiation absorbing properties such as titanium nitride according to CVD method or vacuum deposition method or the like; a technique of forming an antireflective coating on a substrate by applying an organic polymer solution containing a light-absorbing dye dispersed or dissolved therein to the surface of the substrate; and a technique of using, as an antireflective layer, a radiation absorbing polymer wherein a chromophore of dye is chemically bonded to a backbone polymer, or a polymer which itself has a radiation absorbing property. As to the technique of using a radiation absorbing polymer and the materials used for it, related descriptions are given in, for example, Japanese Laid-open Patent Publication Nos. H6-75378 and H6-118656, WO 9412912, U.S. Pat. Nos. 4,910,122 and 5,057,399, etc. Recently, organic materials, particularly those wherein a chromophore is chemically bonded to a polymer skeleton, are being regarded as most promising, and then research and partly application have been being examined.
A general resist patterning process using the above-described organic antireflective layer is conducted in the following manner. Firstly, a solution for forming the antireflective layer is applied to a substrate and baked to thereby make the antireflective layer insoluble in a solvent for photoresist. Secondly, a photoresist coating is formed on the antireflective coating and, after subjecting to processes of exposure, development, etc., there is obtained a resist pattern on the antireflective layer. Then, the antireflective coating of the resist-free areas where the originally applied resist layer has been removed by the development is removed by dry etching.
Many conventionally known radiation absorbing polymers wherein a dye is chemically bonded to a skeletal polymer have a low solubility in solvents used for resists, and hence solvents being different from those used for resists, such as cyclohexanone, are often employed as a solvent for the radiation absorbing polymer. However, in case that a solvent used for forming the antireflective coating is different from that for photoresist, there may arise problems that process steps for forming the antireflective coating in manufacturing integrated circuits increase in number, process equipments become more complicated and, in some cases, properties of the resist layer themselves are adversely affected. For example, when the antireflective coating and the photoresist layer are formed by using the same coating apparatus as is often conducted, the solvent for photoresist composition must fully be washed off from the coating apparatus before coating the antireflective coating composition. Otherwise, materials for forming the antireflective coating might be precipitated due to the influence of mixing of the antireflective coating composition and remaining photoresist solution upon coating the antireflective coating composition. The precipitate thus formed might close up pipes for waste liquor, or might scatter as fine powder and deposit on the resist surface coated or antireflective coating surface, resulting in deterioration of quality such as deformation of resist pattern. Further, since two different solvents are used, two pipe lines for feeding a solvent for washing backside and periphery of substrate might, in some cases, be required; one line for antireflective coating, and the other line for resist. For example, with an antireflective composition using a polymer described in the aforesaid Japanese Laid-open Patent Publication No. H6-75378 wherein an amino aromatic compound is chemically bonded to a polymer skeleton having acid anhydride groups, there involves a problem that, since the composition well dissolves in cyclohexanone and scarcely dissolves in a solvent for resist, there is a disadvantage that edge rinsing is hard to be conducted by using the same coating apparatus as is used for coating the resist. In addition, an antireflective coating composition containing a low molecular weight dye dispersed in a polymer has also been developed. Such composition, however, often causes unevenness in coating thickness when coated on a surface of a substrate with difference in level, thus these problems are being desired to be improved. As is described hereinbefore, there has been eagerly desired to provide a radiation absorbing polymer which has a strong radiation absorbing property for predetermined wavelength radiation and shows excellent photo-lithographic processability, which is soluble in the same solvent as that used for photoresist, and which can form a uniform coating in thickness on a substrate with complicated uneven surface; a film forming composition containing the radiation absorbing polymer; and an antireflective coating formed from the film forming composition and having good properties.
It is, therefore, an object of the present invention to provide a radiation absorbing polymer adapted for forming an antireflective coating which shows high solubility for a solvent for photoresist, good uniformity coating thickness on a uneven surface, high antireflectivity, good adhesion, good dry etch-ability and good heat resistance, which enables one to form a resist pattern with excellent resolution, and to provide a process for preparing the polymer.
Another object of the present invention is to provide an antireflective coating which shows high antireflectivity, good adhesion, good dry etch-ability and good heat resistance, which enables one to form a resist pattern with excellent resolution through improved manufacturing steps.
A further object of the present invention is to provide a film forming composition adapted for forming the antireflective coating which can form an uniform antireflective coating in thickness even on a surface of a substrate with difference in level.